1. Technical Field
The present invention generally relates to piezoelectric element units suitable for ejecting liquid droplets such as ink droplets, manufacturing methods of the same, and liquid ejecting heads using the same. In particular, the invention relates to a configuration for soldering a piezoelectric element group to a wiring member that supplies a driving signal to a piezoelectric element included in the group.
2. Related Art
An example of liquid ejection head is an ink jet recording head (hereinafter, merely referred to as a recording head) including a passage unit provided with a pressure chamber, a reservoir, and the like; a piezoelectric element unit disposed at the rear surface of the passage unit and having a plurality of vibrators (elements) that cause a variation in volume of the pressure chamber; and a case having therein a housing space for accommodating the piezoelectric element unit, the tip end thereof being bonded to the passage unit.
In the piezoelectric element unit, for example, an electrode formed on the surface of a piezoelectric element is connected to a film-like flexible cable (a kind of wiring members). The flexible cable is electrically bonded to a wiring substrate that supplies a drive pulse. The drive pulse is supplied to the electrode of the piezoelectric element unit through the flexible cable (e.g., see JP-A-11-277745).
In recent years, this kind of recording head tends to have small components to meet demands on reduction in material cost and densification of components. However, as the components become small, the electrodes and terminals thereof become small. This may reduce the bonding area between these components, and degrade the bonding force therebetween obtained by solder bonding. As a result, particularly at the bonding portion where the electrode of the piezoelectric element is soldered to a terminal of the flexible cable, the flexible cable may be detached due to a bending stress that is generated when the flexible cable is bent during assembly. In addition, in such a piezoelectric element unit, a portion of the unit at a rear end side of the bonding portion for the flexible cable disposed at a tip end side is fixed to a fixing plate for fixing the piezoelectric elements with a UV-curable adhesive or the like. This fixing for reinforcement, however, may not prevent the detachment from occurring at the bonding portion.